Tissue biopsies, one type of interventional procedure, are usually performed on an out-patient basis by sedating a patient and inserting a needle through the skin and into the tissue of interest. To increase success, a medical imaging device, which will be generally referenced as an “imager,” is used to guide needles to a target area in the patient, from which a tissue biopsy is to be taken. Any one or more of various different types of imaging modalities may be used depending on a number of factors, including tissue type, anatomic characteristics of the target tissue, biopsy technique for optimal sampling of the target tissue, physician preference, the modality that allows for safe and accurate placement of biopsy needle with documentation that the biopsy specimen was obtained from the target tissue, and lesion conspicuity and visualization of adjacent anatomic structures.
In a typical image guided biopsy procedure, a patient is placed on a couch of an imager in the position that yields the greatest access to the pathology and is mildly sedated. The couch moves the patient into and out of the field of view of the imager. The patient is scanned in this position to locate the approximate region of the area of interest, such as a suspected tumor. Once these images are reviewed, an externally applied marker is affixed to the patient to identify the location of interest, and additional images of just this area are taken.
Interventional procedures such as tissue biopsies are preferably performed outside of the imager. Typically, the size and/or shape of the image does not allow for the procedure to be performed inside the imager. Therefore, after obtaining these localization images, the patient is removed from the imager and the site for insertion of a biopsy needle is prepped and draped for incision. The patient is administered a local anesthetic at the site of the needle entry and a radiologist begins to place the needle into position. To confirm proper trajectory of the needle, the patient is moved back into the imager and images are acquired at the site of entry of the needle. The needle appears in the images. Once this status image is taken, the patient is removed from the imager and the needle is advanced along the trajectory. As the needle continues to be inserted, the patient is repeatedly moved or backed into the imager to capture additional images to confirm the trajectory and position of the needle, until the radiologist confirms that the tip of the biopsy needle is at the target tissue. Sample extraction then occurs and the tissue is sent to pathology for analysis of cells.
This conventional image guided procedure is very time consuming and involves a great deal of time to acquire the images and radiation exposure to the patient. In addition, the methodology is not well defined and requires a fairly steep learning curve.
Several types of systems have been developed to improve the targeting for a biopsy procedure. For example, one system uses a mechanical arm to hold the needle. The position of the arm is registered with the coordinate space of the imager, meaning that the position of the arm, and thus a needle held by it, is known with reference to a diagnostic image of the patient that is taken while the patient is on a couch that moves in and out of the imager. In another example, an MR imager incorporates a system in which the position of a biopsy needle is continuously tracked and displayed on images. However, in order to maintain registration between the patient and the images, the procedure must be performed inside the scanner. Furthermore, the needle tracking component can only be used with the particular MR imaging system.